Standard Bf : The student will demonstrate an understanding of the interrelationships among organisms and the biotic and abiotic indicators of their environments. : The student will demonstrate an understanding of the interrelationships among organisms and the biotic and abiotic indicators of their environments.

Chapter 15 Populations Section 1 How Populations Grow

What is a Population? A population consists of all the individuals of a species that live together in one place at one time. A population consists of all the individuals of a species that live together in one place at one time. Demography – the statistical study of all populations Demography – the statistical study of all populations Study the composition of a population and try to predict how the size of the population will change Study the composition of a population and try to predict how the size of the population will change

Three Key Features of Populations Population size – most important feature –can affect the population’s ability to survive Population size – most important feature –can affect the population’s ability to survive Population density – the number of individuals that live in a defined space Population density – the number of individuals that live in a defined space #of individuals = #of individuals = area(units) area(units) population density population density

Dispersion – the way the individuals of the population are arranged in an area or a volume Dispersion – the way the individuals of the population are arranged in an area or a volume Population dispersion patterns influence the rate of gene flow among and between species Population dispersion patterns influence the rate of gene flow among and between species

Gene Flow Migration-the movement of individuals to or from a population (immigrants add alleles and emigrants subtract alleles Migration-the movement of individuals to or from a population (immigrants add alleles and emigrants subtract alleles Gene flow the movement of alleles into or out of a population Gene flow the movement of alleles into or out of a population

Three main patterns of dispersion are possible within a population Three main patterns of dispersion are possible within a population Randomly spaced – the location of each individual is self- determined or determined by chance within an area or volume Randomly spaced – the location of each individual is self- determined or determined by chance within an area or volume Evenly spaced – they are located at regular intervals – territoriality and intraspecies competition for limited resources lead to individuals living at specific distances from one another Evenly spaced – they are located at regular intervals – territoriality and intraspecies competition for limited resources lead to individuals living at specific distances from one another

Clumped distribution – individuals are bunched together in clusters – may live close together in groups in order to facilitate mating, gain protection, or access food Clumped distribution – individuals are bunched together in clusters – may live close together in groups in order to facilitate mating, gain protection, or access food Each one reflects the interactions between the population & environment Each one reflects the interactions between the population & environment

Plant dispersion Plant also exhibit the same dispersion pattern as those of animals Plant also exhibit the same dispersion pattern as those of animals Most common is clumped dispersion pattern Most common is clumped dispersion pattern Plants close together would compete – uniform dispersion Plants close together would compete – uniform dispersion Random – adapted to a variety of conditions and seeds windblown Random – adapted to a variety of conditions and seeds windblown

Survivorship curves Is a generalized diagram showing the number of surviving members over time from a measured set of births Is a generalized diagram showing the number of surviving members over time from a measured set of births Give information about the life history of a species Give information about the life history of a species

Type I common among large mammals – behavior common –parental care Type I common among large mammals – behavior common –parental care Type II – roughly equal at all ages birds, small mammals Type II – roughly equal at all ages birds, small mammals Type III – high birth rate/ high infant mortality rate Type III – high birth rate/ high infant mortality rate Ex. Invertebrates, fish, plants Ex. Invertebrates, fish, plants

Modeling Population Growth Population model- a hypothetical population that attempts to exhibit the key characteristics of a real population Population model- a hypothetical population that attempts to exhibit the key characteristics of a real population Demographers can predict what might occur Demographers can predict what might occur Three stages of complexity Three stages of complexity

Tagging Monarch Monarch Watch was formed in 1992 Monarch Watch was formed in 1992 Essential Question: What can we learn about migration from tagged monarchs? Essential Question: What can we learn about migration from tagged monarchs?

Population grows when birthrate is greater than death rate – P.G. difference between the birthrate & the death rate Population grows when birthrate is greater than death rate – P.G. difference between the birthrate & the death rate Exponential growth curve – a curve in which the rate of population growth stays the same – increase steadily Exponential growth curve – a curve in which the rate of population growth stays the same – increase steadily To calculate the # of individuals that will be added –multiply the size of the current pop.(N) by the rate of growth (r) To calculate the # of individuals that will be added –multiply the size of the current pop.(N) by the rate of growth (r)

Carrying capacity (K) –the population size that an environment can sustain Carrying capacity (K) –the population size that an environment can sustain Carrying capacity can change when the environment changes Carrying capacity can change when the environment changes Population crash is a dramatic decline in the size of a population over a short period of time Population crash is a dramatic decline in the size of a population over a short period of time Limiting factor – has the greatest effect in keeping down the size of population Limiting factor – has the greatest effect in keeping down the size of population

Density-dependent factors –the effect of limited resources will affect the population density that uses them Density-dependent factors –the effect of limited resources will affect the population density that uses them Competition, predation, parasitism and disease are limiting factors Competition, predation, parasitism and disease are limiting factors Logistic model – a population model in which exponential growth is limited by a density-dependent factor Logistic model – a population model in which exponential growth is limited by a density-dependent factor

Competition for food, shelter, mates, and limited resources tends to increase as a population approaches its carrying capacity Competition for food, shelter, mates, and limited resources tends to increase as a population approaches its carrying capacity Accumulation of wastes also increases Accumulation of wastes also increases

Growth Patterns in Real Populations Density-independent factors – growth limited by environmental conditions Density-independent factors – growth limited by environmental conditions Weather & climate are the most important Weather & climate are the most important Some organisms grow exponential, while others grow logistic growth model, Some organisms grow exponential, while others grow logistic growth model, Some will use both at different times as the environment changes Some will use both at different times as the environment changes

Rapidly Growing Populations R-strategists – grow exponentially when environmental conditions allow them to reproduce R-strategists – grow exponentially when environmental conditions allow them to reproduce R-strategists have short-life span, reproduce early, have many offspring which are small and mature rapidly with little or no parental care R-strategists have short-life span, reproduce early, have many offspring which are small and mature rapidly with little or no parental care

Slowly Growing Populations K-strategists- population density is usually near the carrying capacity (K) of their environment K-strategists- population density is usually near the carrying capacity (K) of their environment Long life span, slow maturing process, reproduction late in life, extensive care of their young, tend to live in stable environments Long life span, slow maturing process, reproduction late in life, extensive care of their young, tend to live in stable environments

Population Pyramids profile.com/data/ani_ceu_ pop.htm profile.com/data/ani_ceu_ pop.htm profile.com/data/ani_ceu_ pop.htm profile.com/data/ani_ceu_ pop.htm

Homework P. 325 Section 1 review all questions P. 325 Section 1 review all questions P. 335 Questions 1-3,6,10,13,16, 18 P. 335 Questions 1-3,6,10,13,16, 18

How Populations Evolve Section 2 Hardy-Weinberg principle –the frequencies of alleles in a population do not change unless evolutionary forces act on the population Hardy-Weinberg principle –the frequencies of alleles in a population do not change unless evolutionary forces act on the population Holds true if population is big enough that members will not mate with relatives Holds true if population is big enough that members will not mate with relatives

Five principle evolutionary forces: mutation, gene flow, nonrandom mating, genetic drift, and natural selection Five principle evolutionary forces: mutation, gene flow, nonrandom mating, genetic drift, and natural selection Can cause the ratios to differ significantly from predicted by the Hardy-Weinberg principle Can cause the ratios to differ significantly from predicted by the Hardy-Weinberg principle

Mutation Mutation rates in nature are very slow Mutation rates in nature are very slow Not all mutation result in phenotype changes Not all mutation result in phenotype changes Several codons can code for the same amino acid Several codons can code for the same amino acid Mutation is a source of variation Mutation is a source of variation

Gene Flow Migration-the movement of individuals to or from a population (immigrants add alleles and emigrants subtract alleles Migration-the movement of individuals to or from a population (immigrants add alleles and emigrants subtract alleles Gene flow the movement of alleles into or out of a population Gene flow the movement of alleles into or out of a population

Nonrandom Mating Prefer to mate with others that live nearby or are of their own phenotype Prefer to mate with others that live nearby or are of their own phenotype Mating with relatives (inbreeding) causes a lower frequency of heterozygotes than predicted by Hardy- Weinberg principle Mating with relatives (inbreeding) causes a lower frequency of heterozygotes than predicted by Hardy- Weinberg principle Also when organisms choose based on certain traits Also when organisms choose based on certain traits

Genetic Drift Genetic drift – the random change in allele frequency in a population Genetic drift – the random change in allele frequency in a population Changed by chance events causing isolation Changed by chance events causing isolation Genetic uniformity can reduce disease resistance Genetic uniformity can reduce disease resistance Lack of genetic diversity may hasten extinction Lack of genetic diversity may hasten extinction

Natural Selection Causes deviations from H-W proportions by changing frequencies of alleles Causes deviations from H-W proportions by changing frequencies of alleles Frequency will increase or decrease, depending on allele’s effects on survival & reproduction Frequency will increase or decrease, depending on allele’s effects on survival & reproduction Sickle cell anemia in US Sickle cell anemia in US One of the most powerful agents of genetic change One of the most powerful agents of genetic change

Genetic conditions are not eliminated by natural selection because very few of the individuals bearing the alleles express the recessive phenotype Genetic conditions are not eliminated by natural selection because very few of the individuals bearing the alleles express the recessive phenotype

Natural selection enables individuals who express favorable traits to reproduce & pass those traits on – acts on phenotypes not genotypes Natural selection enables individuals who express favorable traits to reproduce & pass those traits on – acts on phenotypes not genotypes Selection cannot operate against rare recessive alleles unless heterozygous individuals are common & produce homozygous offspring Selection cannot operate against rare recessive alleles unless heterozygous individuals are common & produce homozygous offspring

Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes Polygenic trait – a trait that is influenced by several genes Polygenic trait – a trait that is influenced by several genes Normal distribution-a range of phenotypes clustered around an average value Normal distribution-a range of phenotypes clustered around an average value

Directional Selection Eliminates one extreme from a range of phenotypes, alleles for that trait become less common Eliminates one extreme from a range of phenotypes, alleles for that trait become less common Directional selection – the frequency of a particular trait moves in one direction in a range Directional selection – the frequency of a particular trait moves in one direction in a range Has a role in the evolution of a single- gene traits Has a role in the evolution of a single- gene traits

Stabilizing Selection When selection reduces extremes, the frequencies of the intermediate phenotypes increase When selection reduces extremes, the frequencies of the intermediate phenotypes increase Distribution becomes narrower tending to”stabilize” the average by increasing the proportion of similar individuals Distribution becomes narrower tending to”stabilize” the average by increasing the proportion of similar individuals Very common in nature Very common in nature